In anatomical studies aimed at tracing the path of body sensory signals between the location of a stimulus and the brain cortex, it is common to use an iontophoresis probe to inject a controlled and constant rate of ions into the region of the body under study with a resulting effect upon the cortex area responsive to that region of stimulation permitting the correlation of source and receptor sights. The iontophoresis probe typically comprises a pipette having a very narrow opening, as small as 5 microns, through which ions generated within the probe are applied to the anatomical specimen. The ions are generated by electrolytic reaction within the pipette from voltage applied to it from an external source. Typical electrolytes include HRP (HORSERADISH, PEROXIDASE) or TPL (TRITIATED PROLINE OR LEUCINE).
In effect, the electrolyte converts the electrical voltage applied to the pipette into an ionic current which then flows into the body when the body is made a part of the circuit with the current source. It is important to maintain a constant flow of ions at a relatively low current level, typically measured in small numbers of microamperes, for valid and accurate use of the iontophoresis technique. While it is possible to maintain well regulated currents of this level under normal conditions, the pipettes used in iontophoresis, particularly those with small apertures, are subject to clogging through blood clots, air bubbles, or other mechanisms. Such clogging drastically increases the impedance of the pipette circuit through the electrolyte and body under study from megohm ranges up to near open circuit conditions. Such blockages can impede or eliminate the flow of ions from the pipette to the body resulting in abandonment of the experiment